This invention relates to a photosensitive lithographic printing plate and a photosensitive composition used in such a printing plate. More particularly, it relates to a photosensitive lithographic printing plate having been improved in the loss of dye or pigment (i.e., color fading) in the resist images, which may occur during development, washing with a plate cleaner, printing with ultraviolet curing ink, or the like, and also to a photosensitive composition used in such a printing plate.
Heretofore, photosensitive lithographic printing plates obtained by mixing a diazo resin, a binder resin, etc. to prepare a photosensitive composition, and applying the composition to a hydrophilic metal plate, paper or, preferably, aluminum plate, etc. have been widely utilized in the art.
In such an instance, a coloring matter is incorporated into the photosensitive composition in order to make the images visible during developing or printing. For example, there have been used dyes such as acridine dyes, cyanine dyes, styryl dyes and triphenylmethane dyes, or pigments such as phthalocyanine.
However, these dyes having been conventionally used may cause eluation of dye (loss of dye) from image portions when developing is carried out for a long period of time, particularly when the developing is carried out by repeatedly rubbing a plate surface with a cellulose sponge or the like impregnated with a developing solution, or when washing with a plate cleaner or the like containing an organic solvent, a surface active agent, etc. is repeated during printing, or when printing is carried out with use of ultraviolet (UV) curing ink, and there have been a difficulty in determination of presence of resist image to cause difficulty in practical use.
In the case of the pigments, on the other hand, the loss of pigment may not occur. However, because they are insoluble in the organic solvent used when the photosensitive composition is applied, they are used in the dispersed state to bring about insufficient coating properties, and because they are insoluble in nature, they do not dissolve in the developing solution to give also insufficient developing performances.